1. Field of the Invention
The present invention relates to a thermal transfer image receiving sheet. More specifically, the present invention relates to a new thermal transfer image receiving sheet having an excellent antistatic property.
2. Description of the Related Art
Various types of the thermal transfer methods are known. As one of the above methods, there is known the following sublimation thermal transfer method. More specifically, a thermal transfer sheet is prepared in such manner that a sublimation dye as a recording agent is supported by such a substrate sheet as a paper, or a plastic sheet. Using the thus prepared thermal transfer sheet, various full color images are formed on a thermal transfer image receiving sheet enabling to be dyed by the sublimation dye, such as a thermal transfer image receiving sheet manufactured by forming a dye receptor layer on the surface of a paper or plastic film.
In the sublimation thermal transfer method, a thermal head of a printer is used as heating means. With the use of the thermal head of the printer, the multicolored dots comprising three or four colors are transferred to the thermal transfer image receiving sheet by heating for a short time, thus reproducing full color image of the original by the above multicolored dots.
In the above sublimation thermal transfer method, the used coloring material is a dye. Since the thus formed image is very clear and excellent in transparency because of the dye used as the coloring material, the obtained image is excellent in the reproduction of the intermediate color and the gradation similarly to an image obtained by the conventional offset printing or gravure printing, furthermore, the high quality of image comparable to the full colors photographic image can be formed.
Although a plastic sheet, a laminated sheet composed of a plastic sheet and paper, a synthetic paper or the like are used as the thermal transfer image receiving sheet in the above sublimation thermal transfer method, a plain paper such as a coated paper (an art paper), a cast coated paper, a PPC paper is desired to be used as the substrate sheet for the thermal transfer image receiving sheet, in order to expand the use of the thermal transfer image receiving sheet into a general office field. Furthermore, since the sublimation thermal transfer method is effective in forming an OHP image, there is a demand for a thermal transfer image receiving sheet for the OHP which is capable of forming a quality image excellent in transparency or the like.
The above thermal transfer image receiving sheet has the following problems: more specifically, since various materials used for the thermal transfer image receiving sheet, especially the above various materials used as the substrate sheet have a high surface electrical resistance, the thermal transfer image receiving sheet is easily charged with static electricity by friction when the substrate sheet is manufactured, when a cushion layer, a dye receptor layer, a back surface layer (a slip layer) or the like is formed, when the thermal transfer image receiving sheet is rolled up or cut out, or when the thermal transfer image receiving sheet is put in cartridges or cases. Furthermore, while the thermal transfer image receiving sheet is used, the thermal transfer image receiving sheet is easily charged with static electricity when the thermal transfer image receiving sheet contacts with feeding rolls or thermal transfer sheets, or when the thermal transfer image receiving sheet is peeled off the thermal transfer sheet after printing.
When the thermal transfer image receiving sheet is charged with static electricity, dusts or the like are easily adhered on the surface thereof. Besides, when the thermal transfer sheet clings to the thermal transfer image receiving sheet due to the static electricity, only the thermal transfer sheet is stretched by the thermal head and it may be wrinkled. Such adhesion of the dusts and wrinkles of the thermal transfer sheet result in a deteriorated resolution of the formed image. In addition, the thermal transfer sheet is also charged with static electricity owing to the charged thermal transfer image receiving sheet, and thus they cling to each other to lower a conveying ability of the thermal transfer sheet and the thermal transfer image receiving sheet. Furthermore, in worse case, it is sparked or the body of human being is shocked when the thermal transfer sheet or the thermal transfer image receiving sheet is exchanged or inserted. The above mentioned problem is caused to occur not only in the opaque transparent thermal transfer image receiving sheet essentially comprising a paper substrate material but also in the transparent thermal transfer image receiving sheet used for the OHP or the like.
In order to prevent the above mentioned charge with static electricity from occurring, it is known that a surface active agent is applied on the front surface of the thermal transfer image receiving sheet to form an antistatic layer. However, the use of the surface active agent has caused a problem in which adhesiveness occurs in the surface of the thermal transfer image receiving sheet, or the antistatic layer thus formed is transferred to the back surface layer of the thermal transfer image receiving sheet when the thermal transfer image receiving sheet is stored in the form of piling or rolling. Furthermore, together with the above problem, the antistatic effect is lowered as time passes.
There is known another method in which a conductive layer is formed by using a conductive agent such metal oxides as a conductive carbon black or a tin oxide, and a binder. However, the above conductive agent has a black color or the like, thus deteriorating the appearance of the obtained thermal transfer image receiving sheet.
As the method to overcome the above problem, there is proposed, in the Japanese Patent Application Laid-Open (Kokai) No. 2-182,491, a method in which the antistatic layer is formed by using an acrylic resin having a functional group of a quaternary ammonium salt. However, since the above mentioned material forming the antistatic layer has basically inferior adhesiveness to the substrate or other resin, useful material is very restricted within a narrow range. Furthermore, the antistatic property varies occasionally under the circumstances.